1. Technical Field
The invention relates to a carriage guide mechanism that is used in a printer to guide a carriage that carries a printhead in a main scanning direction perpendicular to the recording paper transportation direction. More particularly, the invention relates to a carriage guide mechanism that is used in a printer to guide a carriage with no play or vibration.
2. Related Art
Serial printers such as roll paper printers used to issue receipts and print journal reports move a carriage bidirectionally in a main scanning direction that is perpendicular to the recording paper transportation direction while simultaneously driving a printhead that is carried on the carriage to print on the recording paper. If there is a gap between the carriage and the guide shaft that guides the carriage in the main scanning direction, there is some play in the carriage when the carriage is moved, resulting in vibration or chatter that renders the printing position on the recording paper of the printhead carried on the carriage unstable and results in such problems as a drop in print quality. Particularly when an inkjet head is used, this causes the position where the ink droplets discharged to the recording paper and to become unstable and easily results in a drop in print quality.
To solve this problem, the recording device taught in Japanese Unexamined Patent Appl. Pub. JP-A-H04-347676 eliminates play between the carriage guide shaft and the carriage by supporting the carriage guide shaft by means of a bearing that combines a rolling bearing and a sliding bearing.
The inkjet printer taught in Japanese Unexamined Patent Appl. Pub. JP-A-2006-123456 prevents play between the carriage and a guide rail by holding a guide rail (guide shaft) from three directions by means of a bearing attached to the carriage.
With the carriage guide mechanism that uses a rolling bearing to guide the carriage as taught in the related art, the guide shaft is circular in section, and the outer ring of the rolling bearing attached to the carriage makes point contact with the circular outside surface of the guide shaft. With this configuration the carriage moves while the rolling bearing rolls along the round outside surface of the guide shaft. If the rolling bearing is disposed to hold the outside circumference of the guide shaft from plural directions, such as from three directions, play and vibration of the carriage in directions separating away from the guide shaft can be reliably prevented. However, play and vibration in the direction in which the carriage pivots on the round guide shaft cannot be effectively suppressed. Particularly if the guide shaft is slender in the direction perpendicular to the direction of carriage movement (that is, the recording paper transportation direction), movement of the carriage around the axis of the guide shaft is amplified with distance and is particularly great at the parts of the carriage farthest from the guide shaft. As a result, the position of the printhead carried on the carriage varies relative to the recording paper, the platen gap may vary greatly in the ink nozzle row direction in the case of an inkjet head, and print quality may drop.